Effect of Hubbard U on Calculations of Magnetic Properties of α″–Fe₁₆N₂

The ordered iron nitride phase α″–Fe₁₆N₂ has long been a candidate giant saturation magnetization material, but first-principles electronic-structure calculations have struggled to reproduce recent observations of high magnetic moment, while calculations of magnetocrystalline anisotropy (MCA) vary significantly. Within the framework of density-functional theory (DFT), a common extension to the usual generalized-gradient approximation (GGA) exchange-correlation (XC) functional is the inclusion of Hubbard parameters U (,J) as GGA+U. A number of previous papers have applied this method to Fe₁₆N₂, each with their own choice of Hubbard parameters. 

The plane-wave DFT code Quantum ESPRESSO was employed to more comprehensively study the effect of the value of Hubbard parameters U, J on the system, particularly with respect to its magnetic properties. Various approaches for setting U, J were compared, including self-consistent calculations via the linear-response method.